Lap winding is known as a method of winding coils which are inserted into a stator of rotating electrical machine. In the lap winding, a plurality of coils is arranged in a circumferential direction of the stator, and parts of adjacent coils are overlapped in a radial direction of the stator. The coils are wound so that inner coil-sides and outer coil-sides of the overlap are alternately exchanged. Coils forming respective poles of respective phases are arranged so that each coil and an adjacent coil are alternately overlapped in the radial direction of the stator while slots into which the coils are inserted are shifted from each other by a predetermined slot pitch. Since the coils are normally made by winding, for example, a copper wire at a multiple number of times, the coils are poor in flexibility thereby to be low in operability in the case where the coils are inserted into the slots.
Accordingly, for example, a method is proposed in which the coils are divided into a plurality of groups and are inserted into the coils in a stepwise manner.
However, one of the rotating electrical machines includes two, large and small, coils having different slot pitches and forming respective poles in each phase. When a method is employed in which the coils are simply divided and inserted into the slots at a plurality of times, the coils which need to be made have the number obtained by multiplying the number of coils before the division with the number of coils divided. Although the operability is improved in the case of insertion of the coils into the slots, man-hours required to manufacture the coils and man-hours required in the arrangement of the coils before insertion are increased. As a result, the increase in the man-hours becomes a factor that inhibits improvement of productivity.